The present invention relates to an opto-electronic device and fabrication method thereof, more particularly to the alignment of a patterned ohmic contact layer in an opto-electronic device.
The ohmic contact layer in question interfaces between an electrode and a diffusion area on the surface of a semiconductor substrate, to ensure an ohmic contact between the electrode and the diffusion area. If the opto-electronic device is a light-emitting diode (LED), for example, the diffusion area is an area from which light is omitted when the electrode supplies driving current. If the device is an LED array, there are a plurality of such areas, with respective electrodes.
Especially in the case of an LED array, the ohmic contact pattern needs to be accurately aligned with the diffusion areas. This is difficult, because the diffusion areas are conventionally defined by a diffusion mask, and the ohmic contact layer is patterned by an etching mask. The two masks are formed in different steps in the fabrication process, and their mutual alignment is almost never perfect. Mask alignment error, and the resultant misalignment of the ohmic contact pattern with the diffusion pattern, can cause such problems as inadequate electrical contact between electrodes and diffusion areas, and short circuits between electrodes and non-diffusion areas. These problems are particularly acute in high-density arrays, where they significantly reduce manufacturing yields and degrade light-emitting characteristics.
LEDs and LED arrays are used as light sources for many purposes. To name one application, LED arrays are used as light sources in electrophotographic printers. The above-mentioned problems present an obstacle to the development of high-quality LED printers with high dot resolution.